Development Of Lightning Low Frequency Magnetic Field Detection System Based On Ferrite Antenna

The strong electromagnetic field radiated by the return stroke of ground lightning will cause a lot of harm.If the strong electromagnetic field with the main radiation frequency of 30 k Hz-300 k Hz can be detected accurately,it can not only improve the positioning accuracy of lightning,but also deepen the understanding of its physical process.In this paper,we design a lightning low-frequency magnetic field detector based on a ferrite antenna,which overcomes the shortcomings of the previous detector,such as large size of detection antenna,narrow band of detection antenna,low gain of signal processing circuit,unstable performance of signal processing circuit.Firstly,based on the LCR analyzer,the influence of the antenna length,the number of the wire and the diameter of the magnetic rod on the resistance,capacitance and inductance of the antenna is analyzed.Secondly,In the performance test of the antenna,For the first time,a test platform was constructed using Helmholtz loop coils,and then the platform was used to perform sensitivity tests on the reception performance of 330 ferrite antennas wound.Based on the sensitivity test,the effects of antenna length,the number of wires and the diameter of the magnetic rod on the receiving performance of the antenna were discussed in 10 k and 100 k circuits,respectively.Finally,the ideal ferrite antenna,signal processing circuit and data acquisition and transmission module are selected to assemble the lightning low-frequency magnetic field detector,and the detectors were deployed in Hainan Province to detect lightning.Based on the detection data,this paper analyze a thunderstorm process in Hainan Province on August 19,2019,and compare and analyze with radar data and TBB data.The research conclusions of this paper are as follows:(1)The resistance range of ferrite antenna is from a few ? to a dozen ?,the capacitance range of ferrite antenna is from a few ?F to a few hundred ?F,and the inductance range of ferrite antenna is from a few m H to a dozen m H.In the process of antenna design,we can increase the number of wire,increase antenna length and magnetic rods diameter appropriately to increase the coupling ability of the antenna and reduce the loss of the antenna,so as to improve the receiving efficiency of the antenna.(2)Under 10 K circuit,the frequency response curve of the antenna is flat,the signal is stable,but the frequency response value is small.The signal U of the antenna is mainly proportional to the signal B.the signal in this circuit can better reflect the characteristics of the lightning and is more conducive to the inversion of the physical process in the return stroke process.The range of antenna frequency response value is about 0.0001 ?0.25 V/n T,and the bandwidth range is about 390 ?555 k Hz.(3)Under the 100 k circuit,the frequency response curve of the antenna has a long rising area and a large frequency response value.The signal U of the antenna is mainly proportional to d B / dt.In this circuit,the pulse signal detected by the antenna is more,and the amplitude is large,which is more conducive to lightning positioning.The frequency response of the antenna ranges from 0.05 to 2 V / n T,and the bandwidth ranges from 616 to 665 k Hz.(4)Increasing antenna length can increase the antenna bandwidth,but it will reduce the frequency response value of the antenna.However,increasing the wires number can increase the frequency response value,but it will reduce the bandwidth.Increasing the magnetic rod diameter can increase the frequency response value and the bandwidth,but it will make the size of the antenna larger.So the selection of the antenna length,the wires number and the magnetic rod diameter needs to be considered in a compromise.(5)At low frequencies,the signal of the antenna is mainly determined by the signal coupled to the antenna.As the frequency increases,the loss of the antenna becomes more and more important.At high frequencies,the signal of the antenna is mainly determined by the antenna loss.(6)The detection data shows that the frequency response value of the large magnetic rod antenna is about an order of magnitude greater than that of the medium magnetic rod antenna.Moreover,the location results of lightning results show that most of the location points are located in the strong echo area of the radar figure and the low temperature area of the TBB figure,which shows that the detection accuracy of the lightning low frequency magnetic field detector in this paper is reliable.